Basics of Topological Editing: Coverages, Map Topology & Topology Rules (Especially for GATE-Geospatial 2022)

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Topological editing ensures that digitized spatial features follow the topological relationships that are wither built into a data model or specified by the user. Examples of topology-based GIS packages include ArcGIS, AutoCAD Map, and MGE. They have similar capabilities in fixing topological errors with geometric features.

Using ArcGIS as an example, it covers three types of topological editing:

This Diagram Shows Three Types of Topological Editing

Topological Editing on Coverages

Topological editing on coverage typically starts by constructing its topology. ArcGIS has the clean command, which not only builds topology but also applies the dangle length and fuzzy tolerance to the entire coverage to remove some digitizing errors.

Editing Using Map Topology

A map topology is a temporary set of topological relationships between the parts of features that are supposed to be coincident. For example, a map topology can be built between a land-use layer and a soil layer so that their outlines are coincident.

The cluster tolerance can snap vertices and lines if they fall within the specified tolerance. Functionally, the cluster tolerance is like the fuzzy tolerance for editing coverages. A large cluster tolerance can unintentionally alter the shapes of lines and polygons.

Editing Using Topology Rules

The geodatabase data model has a total of 25 topology rules for point, line and area features. Editing with a topology rule involves three basic steps.

As with the editing of coverages, the steps of creating a topology, validating the topology rule, and fixing topological errors may have to be repeated before we are satisfied with the topological accuracy of a feature class or of the match between two or more feature classes.

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